Whether the determination of how long one must remain in a leprous house in order to communicate impurity to his clothing is a Biblical law or a Law Communicated to Moshe at Sinai: Eruvin 4a; Succah 5b-6a
Use of the principles of "Gud Achit/Asik" pretending to extend walls to meet ceilings/floors, where legally required: Eruvin 4b; Succah 5b, 6b
Use of the principle of "Dofen Akumah" to consider a surface which is invalid as a roof of a Succah, to be an extended segment of the wall: Succah 5b, 6b